Injection molding machine



C. 10, 1944. A GQESSUNG 2,359,839

INJECTION MOLDING MACHINE Filed Dec. 21, 1942 /N VEN ro e Patentedof.-1o,"1944l UNITED 4s'rirnss PATENT I t l t. I I

Gerald A. (roessling,l St. Louis, litio., assignor to Pro-Phy-Lac-TicBrush Company, Florence,

Mass.,

a corporation of Delaware Appucaaon December 21, 1942, serial No.469,623

` (c1. n so) j 4 Claims.

This invention relates to machines for injection molding or die castingof plastics, and more particularly to the mechanism for forcing theheatsoftened plastic material from an injection cylinder into the moldby means of a ram reciprocable in said cylinder. The invention has forits principal object to increase the plasticizing speed and capacity ofthe injection cylinder without lengthening the stroke of the ram,without loss of injection pressure, and without increasing the powerrequired to operate said ram. Other objects are to provide a moreuniform ow and thorough breaking .up and heating of the mate-- rial inthe injection cylinder. The invention consists in the injection moldingmachine and in the construction, combinations and arrangements of partshereinafter described and claimed.

In the accompanying drawing, which forms part of this specication andwherein like symbols refer to like parts wherever they occur,

Fig. 1 is a central longitudinal section through an injection moldingdevice embodying my invention; and

Fig. 2 is an enlarged fragmentary central longitudinal section throughthe nozzle end of the injection cylinder. o

'I'he device shown in Fig. 1 of the accompanying drawing comprises ahorizontally disposed injection ram or plunger I, which has a taperedworking or forward end la and is secured at its rear end to a uidactuated piston 2 for reciprocation thereby. The piston 2 works in acylinder 3 which is fixed to the rear end of a. supporting housing 4,the piston being actuated by fluid pressure supplied to the cylinderthrough a port 5 at one end thereof and a port 6 at the opposite endthereof. The ram vI extends through the housing 4 beyond the front endthereof and is slidably supported in a. non-rotary bushing 1 mounted insaid housing near the forward end thereof. In accordance with commonpractice, the ram is cooled with Water circulated therethrough by exiblepipes I b communicating therewith.

Rigidly xed to the forward end of the housing 4 coaxial with the ram Iis` an injection cylinder 8 whose bore has a forward or outer endportion 9 of relatively small diameter, an inner or rear end portion I0of relatively large diameter, and a forwardly tapering intermediateportion ll-which connects the large diameter of said bore with the smalldiameter thereof. For coni venience of manufacture and assembly, thecylin der 8 comprises a front section 8a andk a rear section .8b thatare threaded together. the front an axial bore in said spreader issection forming the reduced outer end portion 9 of the bore of saidcylinder and the rear section forming the larger rear end portion I0 ofsaid bore. The smaller forward end portion 9 of the bore of theinjectioncylinder 8 is 'adapted to snugly receive the forward end portion of theram I duringthe forward or pressure stroke thereof, said ram` beingentirely clearI of thesmall portion of said bore at the end of itsreturn stroke. As shown in the drawing, the reduced forward end portion9 of the bore of the cylinder 8 opens at its outer end into theforwardly ltapering. outlet passageway I2a of an injection nozzle I2that is threaded into the front end of said cylinder. Disposed in theadjacent ends of the cylinder 8 and nozzle I2is`a streamlined spreaderor torpedo IZb; and reciprocable in the discharge end of the outletpassageway of said nozzle and an inwardly opening discharge valve I3.that'is spring I3a mounted in said last mentioned bore. The dischargevalve way I3b that opens through the outer end thereof and is adapted tocommunicate with the outlet passageway I 2a of the nozzle I2 when saidvalve is pressed inwardly against the pressure'of the valve closingspring I3a. `The outeror discharge end of the valve I3 is rounded, asyat I3c, to exactly t the correspondingly shaped mouthI Ma of an entranceor gate I4 leading to the mold cavity I5a of a sectional die or mold I5,which is moved by any suitable means passageway I3b therefor with saidentrance or gate.

Mounted for rotary but non-axial sliding movement in the large inner endportion I0 of into communication tu-bular shaft I6 having' a large inneror rear end portion journaled in the rear end of said cylinder,

andin the front portion of the housing 4; `The tubular shaft I 6 iscontinuously rotated by gearing comprising av worm I'I journaled in thehous'- ing 4 and a-worm lgear I8 fixedv to said shaft inside saidhousing. The tubular shaft IB has a forward end portion ISIr of reduceddiameter, thereby forming an' annular space 2I|v .between said reducedportionand thefwall of theflarge inner end portion `Ill 8; and agranular` pound is supplied tosaidannular space bya feed hopper 2I`locatedfabove said cylinder-and in continuous -communication with saidspace closed by a' I3 has a. discharge passage- (not shown) intoengagement with the valve I3 to move the same inwardly in the nozzle I2and bring the discharge of the'boreof the cynndef or powdered moldingrcombular shaft I6 has an external helicalscrew 23 formed thereon thathas a snug working ilt in the smooth large inner end portion I Il of thebore of the cylinder B. 'I'he ram I has a snug sliding fit in the axialbore of the tubular shaft I6, and the forward end of the reducedthreaded portion I9 of said shaft terminates short of the smaller outerend portion 9 of said bore and is tapered as at 24 to provide continuouscommunication between the annular space 20 and said smaller ramreceiving end portions of said bore. As shown in the drawing, theinjection cylinder 8 is heated preferably by means of one or moreelectric band heaters 25 which t around said cylinder between the inletopening 23 and the discharge nozzle I2.

By the arrangement described, molding material flows from the feedhopper through the inlet opening 22 in the heated injection cylinder 8into the annular space 20 `therein where it is engaged by thecontinuously rotating feed scre'w 23 and is forced thereby between thetapered end of the tubular shaft I6 and the tapered intermediate portionII of the bore of said cylinder into the reduced outer end portion 9 ofsaid bore. During this forward movement of the molding material, thematerial is thoroughly mixed and uniformly heated to form a plastic orfluid mass, whichvfills the reduced forward end portion 9 of the bore ofthe injection cylinder and the space left in the forward end portion ofthe -bore in the continuously rotating shaft I6 when the ram I isretracted. When it is desired to flll the mold I5, the mold is movedinto contact with the outer end I3c of the discharge valve I3 to placethe discharge passageway I3b thereof into .communication with theentrance or gate I4 of said mold, and iiuid is admitted to the rear endof the plunger or ram actuating cylinder 3 to force the ram forward. Asthe -ram moves forward, it enters the reduced forward end portion 9 ofthe bore of the injection cylinder 8 and forces the fluid plastic insaid reduced portion of said bore around the spreader I2b and outwardlythrough the outlet passageway I2a of the injection nozzle I2 and throughthe discharge passageway I3b of. the valve I3 into the mold I5. Thepiston 2 is then moved rearwardly to retract the ram I and the moldmoves away from the valve I3 permitting the same to close. In accordancewith common practice, automatic controls (not shown) are provided sothat the mold and ram are operated in proper timed relation and inrepeated cycles.

The hereinbefore described injection molding device has numerousadvantages. It greatly increases the quantity of material than can beplasticized in a given length of time without increasing the stroke ofthe injection ram, and it enables the diameter of the cylinder to bein-` creased without loss of injection pressure and without increasingthe power required to operate the ram. The helical feed screw acts as aconveyor to move the molding material for- 'wardly in the injectionlcylinder; and it also exerts a relatively high continuous pressure onthe material regardless of the position of the ram or plunger. Thisscrew` pressure feed also thoroughly mixes the material and insures amore uniform heating thereof and it also dispenses with devicesheretofore employedA for supplying the cylinder with accurately timedand meas-v ured charges of molding compound.

Obviously, the hereinbefore described injection molding machine admitsof considerable modlflcation without departing from the invention.Therefore, I do not wish to be limited to the precise arrangements shownand described.

What-I claimis:

l. In a machine for injection molding of plastics, a heated cylinderhaving'a'n axial bore with an inner end portion of relatively largediameter, an outer end portion of relatively small diameter and atapered intermediate portion connecting the two end portions of saidbore, a tubular member disposed in the large portion of said borecoaxial therewith and having a tapered outer end portion extending intosaid tapered intermediate portion of said bore and terminating short ofthe small portion thereof, the tapered portion of said tubular membercooperating with the tapered intermediate portion of said bore to forman uninterrupted annular passageway therebetween, said tubular memberhaving an external screw rigid therewith snugly fitting the largeportion of said bore, said cylinder having a feed opening communicatingwith the large portion o1' said bore adjacent to the innermost end ofsaid screw, and a ram reciprocable in said tubular member, said ramentering the small portion of said bore during its forward stroke andbeing clear of said small portion at the end of its return stroke.

2. In a machine for injection molding of plastics, a heated cylinderhaving an axial bore with an inner end portion of relatively largediameter, an outer end portion of relatively small diameter and atapered intermediate portion connecting the two end portions of saidbore, a tubular member disposed ln the large portion of said borecoaxial therewith and having a tapered outer `end portion extending intothe tapered intermediate portion of said bore and terminating short ofthe small portion thereof, the tapered portion of said tubular membercooperating with the tapered intermediate portion of said bore to forman uninterrupted annular passageway therebetween, said tubular memberhaving an external screw rigid therewith snugly fitting the largeportion of said bore, said cylinder having a feed opening communicatingwith the large portion of said bore adjacent to the innermost end ofsaid screw, and a ram reciprocable in said tubular member and having aworking end of solid circular section, said end of said ram entering thesmall portion of said bore during its forward stroke and being clear ofsaid small portion at the end of its return stroke.

3. In a machine for injection molding of plastics, a heated cylinderhaving an axial bore with an inner end portion of relatively large'diameter, an outer end portion of relatively small diameter and atapered intermediate portion connecting the two end portions of saidbore, a tubular member disposed in a large portion of said bore coaxialtherewith and having e, tapered outer end portion extending into saidtapered intermediate portion of said bore and terminating short of thesmall portion thereof, said tapered portion of said tubular membercooperating with the tapered intermediate portion of said bore to forman uninterrupted annular passageway therebetween, said tubular memberhaving an external screw rigid therewith snugly tting the large portionof said bore, said cylinder having a feed opening communicating with thelarge por- 2,859,889 .tion of said bore adjacent to the innermost end ofsaid screw, a, ram reciprocable-in said tubular member, said ramentering the small portion of said bore during its delivery stroke andbeing entirely clear of said small portion at the end of its returnstroke, means for reciprocating said ram, means fo'r rotating saidtubular member,

and an injection valve at the discharge end of the small portion of saidbore for preventing discharge of the fluid plastic from and entry of airinto the small portion, of said bore during the return stroke of saidram.

4. In a machine for injection molding of plastics, a heated cylinderhaving an axial bore with aninner end portion of relatively largediameter, an outer end portion of relatively small diameter and atapered intermediate portion connecting the two end portions of saidbore, a tubular member disposed in the large portion of said borecoaxial therewith and having a tapered outer end portion extending intothe tapered intermediate portion of said bore and terminating short ofthe small portion thereof, the tapered portion of said tubular membercooperating with the tapered intermediate portion of said bore to forman uninterrupted annular passageway therebetween, said tubular memberhaving an external screw rigid therewith snugly fitting the largeportionofsaid bore, said cylinder having a feed opening communicatingwith the large lportion of said bore adjacent to the innermost end ofsaid screw, a cooled ram reciprocable in and supportedV by. said tubularmember, said ram entering the small portion of said bore during itsforward strokeand being entirely clear of such portion at the end of itsreturn stroke, means for reciprocating said ram, means for continuouslyrotating said tubular member, whereby said screw is adapted to force thematerial fromrthe large portion of said bore lthrough thetaperingintermediate portion thereof into the small lportion thereof when theplunger is retracted, and an injection valve in the small portion ofsaid bore adapted to prevent the escape of plastic therefrom during thecontinuous feeding movement of said screw.

GERALD A. GOESSLING.

